1. Field of the Invention
The invention related generally to the field of photography, and in particular to apparatus for preventing the loading of a film cassette into a chamber or the like in a camera, for example. More specifically, the invention relates to apparatus to be used with a film cassette having frangible means that initially operates as a spool lock and as a cam for moving a blocking device of the apparatus out of the way of the cassette when the cassette is first loaded into a chamber but which when broken by a fracturing device of the apparatus is rendered inoperative as a spool lock and as a cam.
2. Description of the Prior Art
Commonly assigned U.S. Pat. No. 5,047,794, issued Sep. 10, 1991 and U.S. Pat. No. 5,032,861, issued Jul. 16, 1991, each disclose a film cassette having an internal spool lock that is moved by a cam pin in the loading chamber of a camera from a locking position to a non-locking position as the cassette is inserted into the loading chamber and that is moved by a leaf spring in the loading chamber from the non-locking position to the locking position as the cassette is withdrawn from the loading chamber. Also, the cassette has cam formed on its housing for moving a blocking device in the loading chamber out of the way of the cassette as the cassette is inserted into the loading chamber. However, when a film exposure status indicator of the cassette is in a film exposed (used) position, the status indicator covers the cam. Consequently, the blocking device will engage the cassette to prevent the cassette from being inserted into the loading chamber.
Prior art U.S. Pat. No. 3,784,001, issued Jan. 8, 1974, discloses a film cassette in which there is a frangible connection between a film spool and an internal wall of the cassette. The frangible connection has sufficient strength to prevent the spool from rotating during handling of the cassette prior to use but which will break when a filmstrip wound on the spool is first pulled off the spool. Since the frangible connection is located inside the cassette, there is no visible way of knowing when it is broken.
Prior art U.S. Pat. No. 4,683,870, issued Jul. 28, 1987, discloses a film cassette in which a film spool has a coaxial opening containing a frangible piece. When the cassette is loaded into a camera, a shaft is received in the coaxial opening to fracture the frangible piece to provide a visible indication the cassette is used.